The background description includes information that may be useful in understanding the present inventive subject matter. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed inventive subject matter, or that any publication specifically or implicitly referenced is prior art.
Friction stir welding (“FSW”) is a solid-state welding process in which a rotating tool (hereinafter a “FSW tool”) heats and intermixes two workpieces at a seam. More specifically, the rotating tool has a pin and a shoulder that are pressed into the seam as the tool rotates, producing frictional heat between the tool and the workpieces. Enough heat is generated such that regions of the workpieces plasticize and mix. The shoulder of the FSW tool assists in causing the plasticized regions to intermix, thus joining (i.e., friction stir welding) the workpieces at the seam. The rotating FSW tool travels along the length of the seam to form a weld joint line between the two workpieces. A detailed description of the FSW process can be seen in Friction Stir Welding and Processing, by R. S. Mishra et al (Materials Science and Engineering R 50 (2005) 1-78).
FSW provides numerous advantages over other welding processes, in part, due to the fact that FSW occurs at much lower temperatures and without a filler material. Some of the advantages of FSW include: better mechanical properties at the weld; less porosity, shrinkage, and distortion; little or no toxic fume emissions; no consumable filler material; and ease of automation. However, there are still various problems associated with FSW, including exit holes, and the weight and costs associated with anvils or clamping tools, which are generally required to counteract the force from the FSW tool head.
Numerous methods and devices for friction stir welding are described in the patent literature. US Patent Application Publication No. 2005/0139640 to Kay, for example, describes friction stir welding methods that use multiple passes of the FSW tool. As another example, U.S. Pat. No. 8,056,797 to Packer et al. describes an expandable mandrel that enables multiple friction stir welding tool heads to simultaneously perform welding on the outer surface of a pipe.
All materials and references cited herein are incorporated by reference to the same extent as if each individual reference were specifically and individually indicated to be incorporated by reference. Where a definition or use of a term in an incorporated reference is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply.
Of particular interest in the present application is the simultaneous welding of both sides of an arcuate joint, such as the joint formed by two pipe segments. U.S. Pat. No. 6,419,142 to Larsson describes a FSW device that has two opposing FSW tools (see Larsson FIGS. 5 and 6 and column 5, lines 35-62). However, as best understood by the applicant, it appears Larsson only contemplates simultaneous welding from one side of the joint (the additional welding head merely serves as a backing unit when placed opposite of the joint line with respect to the first welding; see Larsson column 6, lines 25-27). Larsson also fails to provide a friction stir welding device and method for simultaneously welding both sides of a joint at different locations along the joint.
Thus, there is still a need for improved friction stir welding devices and methods.